1. Field of the Invention
The present invention relates to a method for production of silver halide emulsion producing a silver halide emulsion for photographs comprising silver halide grains, and to an apparatus therefor.
2. Description of the Related Art
Various proposals have been provided about technology for producing halogenated grains of a silver halide emulsion for photographs. In formation generally adopted for silver halide grains, a reaction chamber having agitating and mixing equipment is provided in a reactor containing a gelatin aqueous solution, and a silver salt aqueous solution and a halide salt aqueous solution are introduced to this reaction chamber, crystal grain nuclei are formed, and grain growth by physical aging is performed in the reactor.
Usually, grain formation is performed by causing a reaction between silver ion and halide ion in a reaction container having a sufficient volume equipped with an agitator having agitating blades. In this case, efficiency of agitation in the reaction container is important, and for example, agitation methods of various forms as described in Japanese Patent Application Publication Nos. 7-219092, 8-171156 and 4-283741, Japanese Patent Publication Nos. 8-22739 and 55-10545, and U.S. Pat. No. 3,782,954, etc. are proposed.
In order to form silver halide grains (for example, grains having high monodispersibility, grains having high flat platy ratio in case of tabular grains, etc.) that are preferable as silver halide emulsion for photographs, one of functions for which these agitators are required is uniform and instantaneous micro-mixing. In order to realize uniform mixing, a method is often adopted that a silver salt aqueous solution and a halide salt aqueous solution added are diluted using liquid that has already existed in a reaction container before a reaction between both of the solution. However, when sufficient dilution is not performed in this method, usually a silver halide grain emulsion thus obtained is not preferable as photosensitive materials for photographs.
For example, if agitation is inadequate upon addition in a nucleation period in preparation of tabular grains and a solution added is not fully diluted, phenomena such as an increase in percentage of non-parallel three-dimensional twin crystals, or polydispersion of tabular grains, etc. are observed in grown grains. This can be confirmed by decreasing agitation rotational frequency using an agitator given in Japanese Patent Publication No. 55-10545.
In the case where dilution is inadequate in a growth period, new nuclei are formed from a vicinity of an addition opening, and they do not dissolve completely, and as a result, grains formed in a growth period contaminate silver halide grain emulsion obtained. Such a phenomenon especially is notably seen, when high supersaturation growth is performed.
It is thus considered that agitation is important and it is preferable to fully adopt dilution by a bulk liquid. However, usually already formed grain is included in a bulk liquid, and then a problem of recirculation arises that grains formed once circulate in the vicinity of the addition liquid again. If recirculation occurs in a nucleation period, nuclei that are recycled will block formation of new nuclei. Therefore, for example, in order to prepare a grain emulsion having a small grain diameter, even if an amount added for nucleation is increased, a corresponding increase in the number of nuclei may not be realized, but bad influence is given to realize a small grain diameter. Also when monodispersed grain emulsion is to be prepared, since grain diameter difference arises between nuclei that grew by recirculation and nuclei that did not so, polydispersion of nuclei by recirculation arises, which gives bad influence.
In order to solve these problems, a method is proposed in which fine grains prepared beforehand are used for nuclei forming process, nuclei growth process, etc. In this method, a silver salt aqueous solution, a halide salt aqueous solution, and in many cases, a dispersion medium aqueous solution are usually added into a reaction container with a small volume, and while being added, operation of removing fine grains from the reaction container exit is performed continuously in parallel. Fine grains can be used for nucleation and/or nuclei growth.
If this method is used for nucleation, since the problem of recirculation can be controlled, there is an advantage that increase in the number of nuclei may be realized comparatively easily. In order to make the number of nuclei increase as much as possible, it is desirable to make a grain diameter of nuclei formed as small as possible. However, since an agitator used by this method cannot utilize dilution effect by the above described bulk liquid, more powerful agitation is required in order to perform sufficient mix. When agitation is inadequate, for example, in case of preparation of a tabular grain emulsion, a problem of unwilled increase in a ratio of contaminating non-tabular grains occurs. For example, a ratio of non-tabular grains increases as compared with a case where bulk liquid circulation exists in a mixing apparatus described in Japanese Patent Application Publication No. 6-507255 corresponding to U.S. Pat. No. 5,484,697.
In order to obtain a desired silver halide crystal grains based on these facts, it is important to control exactly a number of generation of crystal nuclei, nuclei shape, etc., and for that purpose, various conditions, such as agitation rotational frequency, addition liquid concentration, addition flow rate, amount of solutions that exists in a reactor beforehand, and liquid composition also, need to be properly determined. However, if a production amount, i.e., charged amount, is changed in grain formation in conventional methods, proper various conditions will be varied based on a charged amount, and thereby it is practically difficult to obtain a same grain performance.
On the other hand, according to commercial scene needs in recent years, condition of production is in a situation that diversification of needs forces production of a small amount of lot of products with many forms by a same manufacturing apparatus. Consequently, a scale of a reactor forming a silver halide grains is not necessarily in accord with an amount of scale of production lot unit, and therefore change in a scale of an amount of production in a same reactor provides a resultant factor to vary photograph performance.
There is a method disclosed in Japanese Patent Application Publication No. 2000-292878 as a formation method of silver halide grains in which photograph performance variation is not provided even if charged amount is varied. This is a method for forming silver halide grains using an apparatus having an addition opening of a silver salt aqueous solution and a halide salt aqueous solution to a reaction chamber, the reaction chamber having an agitator in a reaction tank filled with a gelatin solution, and performing grain growth within the reaction tank, wherein a part of reaction in which nucleation is mainly performed is carried out within a mixer currently disposed out of the reaction tank while not having agitator, and subsequently, grain growth is performed after this liquid is introduced into the reaction tank.
However, the method of Japanese Patent Application Publication No. 2000-292878 is a so-called batch tank method, in which grain nuclei formed outside of the reaction tank is stored in one reaction tank, and a silver salt aqueous solution and a halide salt aqueous solution for growing are added into this reaction tank, and subsequently the grain nuclei existing in the reaction tank are grown. Therefore, there occurs a problem that the silver salt aqueous solution and the halide salt aqueous solution added cannot deposit instantaneously to each of the grain nuclei existing in the reaction tank, and thus, practically it is impossible to uniformly grow the grain nuclei.
That is, according to probable consideration, a frequency is small in which grain nuclei existing in a reaction tank have collisional association with ultrafine grains for growth supplied into a reaction tank, in a grain growth method by conventional batch tank methods. Therefore, when a capacity of a reaction tank is large enough as compared to a charged amount, mixing cannot be started actually in an instant, and as a result, grain nuclei and ultrafine grains without any collisional association at all may be formed depending on case. According to this consideration, it is a phenomenon that may happen naturally that a particle size distribution becomes larger by a grain growth method by a batch tank method, and this is unavoidable. Therefore, also in the method of Japanese Patent Application Publication No. 2000-292878, a problem is fundamentally unsolvable that a larger production scale enlarges a grain size distribution.
The present invention is made in order to cancel conventional disadvantage in view of such a situation, and aims at providing a method for production of a silver halide emulsion and an apparatus thereof, in which variation of charged amount accompanying production amount change does not fluctuate photograph performance, flexible production of an optimal amount corresponding to commercial scene needs is attained, and a silver halide emulsion having monodispersibility may be produced with sufficient productivity.
In order to attain the above described objective, the present invention is directed to a method for production of silver halide emulsion, comprising; a grain nuclei forming step of performing a series of continuous operations comprising continuously, instantaneously mixing and causing reaction of a silver salt aqueous solution, a halide salt aqueous solution, and a hydrophilic dispersion medium aqueous solution to form a silver halide grain nuclei, and storing a mother liquor containing the silver halide grain nuclei in a cooled state until the amount of nuclei reaches a desired production amount of the silver halide emulsion; and a grain nuclei growing step of performing at least one series of continuous operation comprising filtering the cooled mother liquor to eliminate unnecessary salt generated in the formation reaction, and to dehydrate and concentrate the filtered mother liquor when the amount of product reaches a desired production amount, and continuously, instantaneously mixing the mother liquor after filtrated and an addition liquid containing silver halide ultrafine grains for growth obtained separately by mixing and reacting a silver salt aqueous solution, a halide salt aqueous solution, and a hydrophilic dispersion medium aqueous solution to grow the silver halide grain nuclei.
In another aspect, in order to attain the above described objective, the present invention is also directed to an apparatus for production of a silver halide emulsion, comprising; a first line in which a silver salt aqueous solution, a halide salt aqueous solution, and a hydrophilic dispersion medium aqueous solution are continuously introduced into an instantaneous mixing reactor of continuous system to form silver halide grain nuclei continuously, and a mother liquor containing the silver halide grain nuclei formed is continuously discharged from the instantaneous mixing reactor, and is stored in a cooled tank; a second line in which an addition liquid containing silver halide ultrafine grains for growth is continuously prepared by mixing a silver salt aqueous solution, a halide salt aqueous solution, and a hydrophilic dispersion medium aqueous solution using an instantaneous mixer of continuous system; and a third line in which the mother liquor stored in the cooled tank is continuously filtrated with a filter to eliminate unnecessary salt generated in the formation reaction of the grain nuclei, and to dehydrate and concentrate the mother liquor, and the mother liquor after filtrated and the addition liquid prepared by the second line are mixed instantaneously by the instantaneous mixer of continuous system and discharged into an aging storage tank.
According to the present invention, in a grain nuclei forming process, a series of continuous operations for forming silver halide grain nuclei by instantaneously mixing and causing reaction of a silver salt aqueous solution, a halide salt aqueous solution, and a hydrophilic dispersion medium aqueous solution, and for storing a mother liquor containing the silver halide grain nuclei in cooled state until the amount of nuclei reaches a predetermined amount of silver halide emulsion product. Thereby since uniform and instantaneously mixing reaction may be performed, and the mother liquor does not recycle into a reaction area in the mixing reaction, formation of silver halide grain nuclei having small diameters with even sizes may be promoted. Since the mother liquor containing formed silver halide grain nuclei is stored in cooled state until the amount of product reaches the desired production amount of a silver halide emulsion, growth of the grain nuclei is controlled until a following grain nuclei growing process is performed. Therefore, in the grain nuclei forming process, a stable formation of silver halide grain nuclei having a small diameter and a uniform size may be performed regardless of variation of charged amount.
Next a series of continuous operations are performed at least once that when the amount of product reaches the desired production amount in a grain nuclei growing process, the cooled mother liquor is filtrated to eliminate, to dehydrate, and to concentrate unnecessary salt generated in the formation reaction, and the mother liquor after filtrated and an addition liquid containing silver halide ultrafine grains for growth obtained separately by mixing and reacting a silver salt aqueous solution, a halide salt aqueous solution, and a hydrophilic dispersion medium aqueous solution are instantaneously mixed continuously to grow the above described silver halide grain nuclei. That is, unnecessary salts that adversely affects stability of formed silver halide grain nuclei, such as unreacted silver salts, unreacted halide salts, by-product salts formed by reaction are eliminated by filtration processing of the mother liquor. This mother liquor after filtrated, and the addition liquid containing silver halide ultrafine grains for grain nuclei growth prepared separately are instantaneously mixed continuously, and growth of grain nuclei is performed. According to the above described method, growth of silver halide grain nuclei is performed uniformly and instantaneously, and moreover if the mother liquor once passes through an area where the mother liquor and the addition liquid are instantaneously mixed, i.e. growth area of grain nuclei, the mother liquor will not pass through the growth range again unless a series of continuous operations are performed next. When a particle diameter of the silver halide grain nuclei is smaller than the desired particle diameter after one time of grain nuclei growing process, a series of continuous operations are repeated until the diameter becomes the desired particle diameter. Therefore, a uniform growth of grain nuclei can be attained regardless of a charged amount.
Thereby variation of charged amount accompanying production amount change does not fluctuate photograph performance, flexible production of an optimal amount corresponding to commercial scene needs is attained, and the silver halide emulsion having monodispersibility may be produced with sufficient productivity.